Hong Kong's anti-extradition movement observed a day of singing protests on Wednesday on the 18th anniversary of the Sept. 11 terror attacks on the World Trade Center in New York, amid growing criticism of police violence from healthcare workers, scientists, and former officials.

Crowds of people gathered in major shopping malls to sing the new anthem of the movement "Glory to Hong Kong," after protesters said on Tuesday there would be no action taken on Wednesday other than singing and chanting.

Chanting "Reclaim Hong Kong!", "Revolution in our time!" and "Stand With Hong Kong!" demonstrators, many of whom weren't wearing masks, also sang the Les Miserables hit "Do You Hear the People Sing?" in English.

Others formed human chains and waved their cell phone flashlights above their heads.

Wednesday's protests were deliberately muted in response to a social media post from the English-language China Daily newspaper, which is backed by the ruling Chinese Communist Party, suggesting that some in the anti-extradition movement were plotting terror attacks to coincide with the Sept. 11 anniversary.

The China Daily Hong Kong edition said the claims, which were posted along with a photo of the Twin Towers under attack, were based on "leaked information" in online chat rooms.

"We condemn the Chinese Communist Party-sponsored media trying to use the aforementioned rumors to trigger the emotions of the American people," some protesters wrote in a statement posted to Facebook on Tuesday.

"The rumors are ... written by the Chinese Communist Party and the HK government, trying to defame HK protestors and to disintegrate the whole movement."

It said the anti-extradition movement in Hong Kong is committed to maintaining good relations with its international allies.

The statement also defended the escalation of protest tactics from peaceful marches to the storming and vandalising of official buildings and the use of batons and Molotov cocktails against riot police by frontline protesters in recent weeks.

"Nonetheless, we have never used any kind of irrational violence against innocent citizens of our city," it said. "[Having suffered] indiscriminate terrorist attacks [from riot police], we know the evil of it and we would not choose such a method even against our shameless government."

"We hereby condemn any sort of terrorist attack," it said. "It is the government, the police and triad members mobilized by them who have been attacking citizens since the beginning of the revolution."

Call for probe

Meanwhile, 27 high-profile figures including former officials and entrepreneurs, called on the administration of chief executive Carrie Lam to begin an independent probe into the anti-extradition movement and its handling, calling the frequent use of batons and pepper spray on protesters not showing any resistance "heartbreaking."

The letter, signed by former welfare minister Stephen Sui, former transport official Yau Shing-mu, telecoms entrepreneur Ricky Wong and the outgoing CEO of the Hong Kong General Chamber of Commerce, Shirley Yuen, also criticised the use of petrol bombs and vandalism by protesters.

It also called for a full investigation into a mob attack on protesters in Yuen Long on July 21, and for a full account of what happened when riot police stormed Prince Edward subway station, indiscriminately attacking train passengers, on Aug. 31.

One of the signatories, the Rev. Yuen Tin-yau, said police have repeatedly used excessive force in quelling protests.

"The violence that the police have been using against demonstrators has exceeded what would be deemed necessary by disciplined forces," Yuen told RFA.

"If the police and demonstrators don't exercise restraint, their mutual hatred will only grow."

"The violence used by the police on July 31 and Aug. 31 was obvious to all Hong Kong people," he said. "However, many members of the public are afraid to complain to the Independent Police Complaints Commission (IPCC) ... [because] they are worried that they will be charged."

"The Government has not responded positively to the demands for an independent inquiry, which has caused disappointment among demonstrators and the wider public," he said.

Long-term effects

The letter came amid growing concerns over the long-term effects of tear gas in densely populated Hong Kong.

Since the anti-extradition protests began in Hong Kong three months ago, the city's police force has fired more than 2,000 tear gas canister at protesters, who have geared up with respirators, water bottles, and containers to try to neutralize the effects.

Despite their best efforts, protesters, passersby, children, elderly people, and pets have suffered ill-effects from the miasma of tear gas that lingers when police deploy the gas in narrow streets and subway stations in a city of seven million people.

Recent research looking at more than 170 frontline reporters who were exposed to tear gas found that more than 90 percent reported persistent coughing, shortness of breath, and coughing up blood, while others suffered rashes, diarrhea, vomiting, and swollen eyes.

Chemical engineers warned on Wednesday that potentially harmful tear gas residue lingers on various surfaces up to three weeks after it is fired, after collecting more than 200 samples from sites in Admiralty, Sheung Wan, Kowloon Bay, Tsuen Wan, and Sham Shui Po, where it was recently fired.

Chemical engineer Michael Lee said tear gas can spread much farther afield than people might think, especially in well ventilated areas, contaminating children's play areas in nearby parks and recreation areas.

"We are worried that the gas chemicals may stick on those facilities in public areas. A child or those elderly doing exercises will be contaminated by the CS ... harming their health," Lee told reporters in a news conference streamed online by the Apple Daily newspaper.

He called on police to stop using tear gas indoors or in poorly ventilated locations, and called on the government to carry out follow-up testing of areas where it has been used.

'Save Hong Kong'

The warning came as a group of healthcare workers published advertisements in major Hong Kong newspapers on Wednesday calling on the government to "save Hong Kong" by acceding to all five of the protesters' demands.

The statement also hit out at "rampant" police violence, which went against humanitarian principles. It cited the refusal of police to allow first-aiders to help the injured during an attack by riot police on train passengers inside Prince Edward MTR station on Aug. 31.

Chief executive Lam last week pledged to formally withdraw amendments to the city's extradition laws that would enable the rendition of alleged criminal suspects to face trial in mainland China.

But protesters say they won't back down until her government launches an independent inquiry, stops describing the protests as "riots," releases and drops charges against hundreds of arrested protesters, and starts a political reform process culminating in fully democratic elections for the post of chief executive and for the city's Legislative Council (LegCo).

The leaderless anti-extradition movement has been increasingly vocal in its support for the Hong Kong Human Rights and Democracy Act, a 2017 bill by Marco Rubio and Chris Smith, co-chairmen of Congressional Executive Commission on China that would "establish punitive measures against government officials in Hong Kong or mainland China who are responsible for suppressing basic freedoms in Hong Kong."

Reported by Lau Siu-fung and Man Hoi-tsan for RFA's Cantonese Service, and by Gao Feng for the Mandarin Service. Translated and edited by Luisetta Mudie.